I think the original telegraph system was a long circuit where all keys and sounders were in series with the loop battery. That is why the old telegraph keys had shorting bars. Every station had a key and a sounder. Each operator kept his key shorted and all sounders were energized. To send a message, an operator opened his key and sent a few 'V's' to alert everyone. Then he sent his message address or call sign of the receiving station. He closed his key and waited for an answer. That is the only way that each station had an equal chance to use the circuit.